Circuit boards are very susceptible to static damage. Static electricity creates a voltage higher than the transmitters of a circuit board can handle, thereby destroying a chip or chips on the circuit board. When a circuit board blows, it is very difficult to determine or fix the chip affected; hence, the entire circuit board must be removed for repair or replacement. Accordingly, it is very important for circuit board storage facilities to be grounded and as static-free as possible.
Circuit boards are usually stored in large shelved cabinets having some sort of anti-static properties and a grounding system; however most of these cabinets are built having the cabinet itself as a major factor in the grounding system. These grounding cabinet structures, which can weigh around 500 pounds, are very large and heavy, making them difficult to transport. Disassembling these cabinets for transportation is not an option since the cabinet is of welded construction and the outside metal of the cabinet is an essential element of the grounding system. Additionally, the complete 500-pound cabinet must be painted to avoid rusting. Not many manufacturers are equipped to move and paint such a large and heavy cabinet. Before painting, several points on the cabinet must be masked off so that paint will not interfere with the conductivity between the stainless steel shelf supports and the outside shell metal. The masked metal is at several of the rivet points that hold the stainless steel supports. This raw, unpainted metal could eventually rust and could lead to a failure of conductivity between the stainless and outer shell. Dirt buildup or loose rivets could also lead to the same sort of failure.
Previous circuit board storage cabinets include making shelves of a static-dissipative plastic mold and adding these shelves to an adjustable track inside a storage cabinet having a grounding system dependant on conductivity of the outside metal shell. These all-plastic shelves do not add conductivity to the grounding system. Additionally, the plastic shelves are not very strong—definitely not as strong as metal. The plastic could bend or disfigure under a heavy weight, and large circuit boards are getting heavier. Several heavy circuit boards on one plastic shelf could potentially bend, disfigure, or break it. These plastic shelves are made of a glass-filled plastic material. While this material is strong, its static-dissipative properties may vary from one point to another on the shelf. Further, previous circuit board storage shelves are dependent upon one another, i.e. to make one shelf taller, the adjacent shelf must be made shorter.
The present invention overcomes the problems of previous anti-static shelves for circuit board storage.